Chromatography columns are typically comprised of a column tube with a top end cell covering the top opening of the tube and a bottom end cell covering the bottom opening of the tube. A chromatography column with variable column height also comprises a plunger or adaptor integrated in the top end cell, which adaptor can be moved to different heights within the column tube. The top end cell (possibly integrated with an adaptor) and bottom end cell comprise further a nozzle assembly adapted to provide chromatography media to the column, sample inlet/outlet, sample distribution means, filter, net, O-rings and seals. The nozzle assembly comprises typically a nozzle tube through which chromatography media in the form of a slurry is provided to the column. The nozzle assembly comprises further normally a slurry outlet used during the unpacking of the column. In U.S. Pat. No. 5,902,485 an access valve suitable for controlling fluid flow into and out of a chromatography column is described. Axial movement of the probe, also known as a nozzle tube, adjusts the valve between a fully open condition, in which both a first conduit extending through the probe and a second conduit defined around the probe are open to the column interior, and a partly open condition in which a sealing component of the probe closes the second conduit. Also further axial movement of the probe provides a fully closed position in which both conduits are closed. The partly open position is useful for packing chromatography media into its column while the third position is useful for unpacking the same.
The movement of the probe into the three different positions is crucial and important. In prior art this is sometimes difficult and not very exact. Some solutions are also rather expensive and require complicated mechanics. In U.S. Pat. No. 5,902,485 one possible way of performing this is shown. In this described system the axial movement of the nozzle tip is performed by use of a screwing mechanism which will not provide very exact positions.